WPF Designer multiple Fixes

Sorry, this a huge commit, but I've fixed many things:

- All Unit Tests, except one are now working.
- Tickets #408 and #192 are now fixed
- A few more Errors during XAML Parsing Process are fixed
- Handling of an Empty Image Control is now fixed (before the changes, you can't adjust the Size of an Image, it always resets to zero!)
- Support that multiple Extensions can create a Context Menu
- Arrange of Items via Context Menu
- Wrapping of a Single Item in a Canvas
- Icons for the Context Menu's (from the Fugue Library)
- Fixes that Controls get Width and Height set when they Enter a Container
- Implement a Formated Text Editor for TextBlock Elements
![image](https://cloud.githubusercontent.com/assets/364896/4843449/4975bcd4-6032-11e4-9049-355ad436aba2.png)
- Allow Extensions to be applied in a specified order
- Redraw Extensions after Enter a Container

![image](https://cloud.githubusercontent.com/assets/364896/4843513/26345fc2-6033-11e4-8e7e-c21ba0b7cd27.png)

- Default Metadata can now be specified with NaN for COntrols where no Height/Width should be set. For Example this is usefule for TextBlocks wich then automaticaly size!